When I change the size of a picture I am keyframing in my video, it changes it for the entire video. The keyframe takes into the account the position of my picture on the video, but the size will only ever stay one size when I need lots of different sizes. Any help/ What am I Doing wrong? If you need more info about what I mean please let me know i'll try to explain it better. Thanks!
You set a keyframe for the position, if I understand you correctly. Did you set a keyframe for scale?
You really need to start here: Getting started with After Effects That link will help you avoid this and a lot of other frustrations you can't even imagine yet.